At first glance, the zenithink seems like a tough nut to crack. No visible screws or seams other than the border between the black plastic surrounding the case and the fake aluminium backing seem to exist. Luckily, the designers saw fit to provide a very easy way to pop it open. I'm going to break it down into a series of steps.

1. Remove the micro SD card, if one is inserted. If you don't, at best the case won't open, at worst the SD card will snap in half and get stuck inside.
2. Face the edge with no buttons, ports or speakers towards you. You should see two small holes on either side, these may be hidden under quality control stickers on some models.
3. Using a piece of thin solid metal like a screwdriver or extended paperclip, push directly into each hole. You will feel resistance, but should be able to comfortably push in about 3mm. After that you will feel stronger resistance, this is the safe limit. You should now be able to free that side of the unit from the back casing. It's better to start on the speaker side, as you will need to maneuver the case around the buttons and switches on the other side.
4. The clips are spring loaded so if you lose control they may snap back into place. If that happens just push the screwdriver/paperclip into the hole again.
5. Be careful with the battery, it is affixed to the back casing and needs to be disconnected from the main unit. Once that is done you are free to admire the various gizmos inside.
   

That's it!